The silicon carbide (hereinafter also referred to as SiC) is expected to be a material for a next generation of power semiconductor devices. Compared with Si, SiC has excellent physical properties such as a threefold band gap, about tenfold breakdown field strength, and about threefold thermal conductivity. When the physical properties of SiC are utilized, an ultra-low-power-loss power semiconductor device that can be operated at high temperatures can be implemented.
There are various high-voltage semiconductor devices in which the properties of SiC are utilized. A Double Implantation MOSFET (hereinafter referred to as a DIMOSFET) in which a p well and a source region are formed by ion implantation is well known as one of the high-voltage semiconductor devices.
The DIMOSFET is easily produced because of use of a planar process of being able to accurately form a channel by the ion implantation method. A power of a drive circuit can be reduced because a gate is driven by voltage control, whereby the DIMOSFET is also excellent for a parallel operation.
However, compared with Si, it is well known that SiC has a significantly high contact resistance between an electrode and a source contact region and p well contact region. In order to solve the problem with the significantly high contact resistance, there is well known a method, in which heating is performed up to about 1000° C. after Ti (titanium)/Al (aluminum) are stacked in the p well contact region while Ni (nickel) is evaporated in the source contact region.
However, when the method is adopted, it is necessary to perform patterning twice to the source contact region and the p well contact region. Additionally, it is necessary to take into account a misalignment of the patterning, which causes an increase in cell size. It is necessary to scale down the cell size in order to reduce an on-resistance of the MOSFET.
For example, Patent Document 1 discloses a method of establishing the contact with different materials in a P+ contact region of a bottom surface of a contact trench provided in a substrate and an N+ type source region of a side surface.